William James, answered from the texts and cited to the page.
The will to believe is, at its core, a defense of the right to hold a belief under specific conditions — not a license to believe whatever one finds agreeable, but a carefully bounded permission that operates only where certain conditions are simultaneously met. The first condition is that the option before you must be live — meaning the hypothesis makes some genuine appeal to your nature, some electric connection with your actual possibilities.1
A hypothesis that strikes you as simply incredible is dead, and the doctrine has nothing to say in its favor. Liveness is not an intrinsic property of a proposition; it is a relation between the proposition and the particular thinker considering it.2 The second condition is that the option must be forced — there must be no standing place outside the alternative.3
If you can remain indifferent, if you can decline to choose and lose nothing by the delay, the option is avoidable and the will to believe does not apply. But where the logical structure of the situation admits no third position, where declining to choose is itself a choice with consequences, the option is forced. The third condition is that the option must be momentous — unique in its opportunity, significant in its stakes, and not reversible if it later proves unwise.4
Trivial options, where a wrong guess costs you only a little time and no vital harm, do not engage the doctrine. Where all three conditions are met — live, forced, momentous — and where the evidence cannot by itself resolve the question, I argue that suspending judgment is not the neutral posture it pretends to be. Religion is my central case.
If the religious hypothesis is true, the person who waits indefinitely for sufficient evidence loses a real good just as certainly as if he had positively disbelieved.5 The sceptic who preaches waiting is not standing outside the game; he is backing the field against the religious hypothesis, taking his own risk, playing his own stake.6 The agnostic rule — keep your willing nature entirely out of the game until the evidence is in — would, if followed absolutely, prevent you from acknowledging certain kinds of truth even if those kinds of truth were really there.
A rule of thinking with that consequence is, for me, simply irrational.7 And if we are empiricists — if we believe no bell in us tolls to announce with certainty that truth is in our grasp — then the solemn command to wait for that bell is a piece of idle fantasticality.8 We act either way; we take our lives in our hands either way. The will to believe is the right to choose our own form of risk, when the option is genuine and the intellect alone cannot resolve it.9
A live hypothesis is one which appeals as a real possibility to him to whom it is proposed.The Will to Believe, pp. 2–4
This shows that deadness and liveness in an hypothesis are not intrinsic properties, but relations to the individual thinker. They are measured by his willingness to act.The Will to Believe, pp. 2–4
But if I say, 'Either accept this truth or go without it,' I put on you a forced option, for there is no standing place outside of the alternative.The Will to Believe, p. 4
if I were Dr. Nansen and proposed to you to join my North Pole expedition, your option would be momentous; for this would probably be your only similar opportunity, and your choice now would either exclude you from the North Pole sort of immortality altogether or put at least the chance of it into your hands.The Will to Believe, p. 4
religion is a forced option, so far as that good goes. We cannot escape the issue by remaining sceptical and waiting for more light, because, although we do avoid error in that way if religion be untrue, we lose the good, if it be true, just as certainly as if we positively chose to disbelieve.The Will to Believe, pp. 26–27
He is actively playing his stake as much as the believer is; he is backing the field against the religious hypothesis, just as the believer is backing the religious hypothesis against the field.The Will to Believe, pp. 26–27
a rule of thinking which would absolutely prevent me from acknowledging certain kinds of truth if those kinds of truth were really there, would be an irrational rule.The Will to Believe, pp. 29–30
if we are empiricists, if we believe that no bell in us tolls to let us know for certain when truth is in our grasp, then it seems a piece of idle fantasticality to preach so solemnly our duty of waiting for the bell.The Will to Believe, pp. 29–30
I simply refuse obedience to the scientist's command to imitate his kind of option, in a case where my own stake is important enough to give me the right to choose my own form of risk.The Will to Believe, pp. 26–27